When I turn the bass up to +6, I hear this vibration or buzzing noise somewhere around the passenger door. I was wondering if any of you experienced this and how this can be fixed... Any comments appreciated.

 

could it be the seat belt making that noise? See if it still happens after fastening the seatbelt

 

Yeah, I had this. There's no "trick" to fixing it; you'll just have to track down what's vibrating. Here's how I did it:

Find a CD with a bass passage that really resonates with the buzz, and use it to test as you go.

Remove the door panel (2 screws in the "oh sh1t" handle, and one behind the "open-close" handle; then carefully pop off the whole thing).

Test for buzzing. If it's gone, maybe the door panel worked loose, or (worst case) maybe you need a new one. This isn't likely though.

If it's still there, just start pressing your hand around on the plastic parts on the door. For me, I found the source was the black corrugated-plastic tube around a wire bundle. By just smushing/cracking/shifting it I was able to eliminate the buzz completely.

Another possible (though unlikely) source is the speaker mount itself.

Good luck!

John